Re: [ATM] Optical flat part II

["Bob May" <rmay@nethere.com>]

Malacara writes more for the professional than the amageur.  As
such, he is thus not really that interested in doing surfaces
other than spherical as only reflector telescopes tend to use
other than spherical surfaces..  We amateurs are off in a
different world for a bit of this with our strange surfaces so we
adapt interferometers to our strange needs and do such tests as
the Ronchi and Foucault tests.  Autocollimation is a nice way fo
turning whatever strange surfaces we are making into nice easy to
test surfaces  because the output of the optical surfaces that we
use end up making a flat wavefront at the output of the full
telescope (exclusive of any flats that may be interdispersed to
change the ddirection of the light path) and thus a large flat
surface which returns the light back down the telescope path does
a marvelous job of doubling the error of the surfaces without
adding any errors of it's own.  Itr also ends up being nice for
refractor telescopes as you get to do color error by using
different colors of KEDs when testing refractor  optics.  With
the new blue LEDs, this ends up giving a real nice set of curves
for the color error!
Bob May
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